An antioxidant compound is any compound or mixture of compounds that, when in contact with the skin, is capable of protect the skin against the action of free radicals.
Antioxidant compounds such as levogyrous ascorbic acid (LAA), popularly known as “Vitamin C”, and proantocianidines (OPC) are widely used in the pharmaceutical and cosmetic industry since, among other characteristics, they act against the free radicals that speed up the aging process and degeneration of the cells.
One of the greatest technical difficulties for the use of the above antioxidant compounds is their instability. The LAA, for example, can easily be oxidized in the presence of atmospheric air, metallic ions or water, thus being transformed into dehydroascorbic acid, in addition to other by-products resulting from the oxidation. Such transformation diminishes its physiological properties, mainly under use conditions where the compound is exposed to the atmospheric air, metallic ions and water such as, for example, when incorporated into a topic solution.
In a simplified way, the instability of an antioxidant is expressed as a decrease of its reducing ability before it is contacted with the skin. In the case of the LAA, its instability is expressed as a compound degradation reaction.
In the case of the OPC's the instability occurs through an oligomerization reaction, followed by polymerization.
The LAA is often used in the form of its salts or esters due to this instability. The compositions prepared in this way attain stability for long periods of time.
Many studies have been carried out in order to obtain an aqueous composition containing stable antioxidant compounds. Some alternatives to stabilize LAA are described in Brazilian Patent Applications PI 9704418-0 and PI 9704728-7, filed by the same applicant of the present application. In said patent applications, processes for stabilizing levogyrous ascorbic acid (LAA) in a water-containing mean are disclosed comprising the step of contacting the LAA with at least one compound capable of forming hydrogen bridges with the LAA.
Another procedure known from the art for stabilizing antioxidants involves the association thereof with the compounds capable of reverting the decomposition reaction, the so-called “reducing agents”. Once again, considering the LAA, for example, said compounds revert the dehydroascorbic acid formation reaction. However, the stabilization through this process results in compositions unacceptable for cosmetic use and many times unsuitable for medicinal use, since the required stoichiometric amount of reducing agents within the stoichiometry limits of the reaction must be too high so that the desired results could be attained. Since the reducing agents are usually selected from sulfur-containing compounds, the high content thereof in the resultant compositions bring about an unpleasant odor and sometimes their use are even legally forbidden. For example, in a solution containing a concentration of 5% by weight of LAA, which is a concentration range generally used in cosmetic-pharmaceutical products, contents of approximately 20% by weight of reducing agent should be required to ensure the LAA stability.
Another prior art reference that can be cited and that teaches the use of reducing agents, is a work published by Wrinkler, B. S. (Biochim, Biophy, Acta, 1117, 1992, pages 287 through 290), in which a compound is described (Glutathion) that can act as a reducer or reducing agent of dehydroascorbic acid by transforming same into ascorbic acid in the stoichiometric form. Through this work it was discovered that it was impossible to keep stoichiometric amounts of the components to produce a cosmetic composition since the Glutathion has an unpleasant odor which is a characteristic of sulphidric compounds.
Therefore, it is an object of the present invention to provide a process for stabilizing antioxidant compounds, that is, anti-free radicals or “anti-radicals”, that makes it possible to overcome the drawbacks common to the known processes, among which the ones that use the so-called reducing agents and, in a special way, that can result in stable, cosmetically more pleasant and more efficient compositions, also suitable for pharmaceutical use.